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Soil Physics 
Laboratory Guide 



By 
W. H. STEVENSON, A. B., B. S. A. 

Professor of Soils, Iowa State College 

and 
I. O. SCHAUB, B. S. 

Assistant Professor of Soils, Iowa State College 




PROFUSELY ILLUSTRATED 



NEW YORK 

ORANGE JUDD COMPANY 

1905 



fiBRARY Ot CJONQREsi 



OUPY 6, 



COPYRIGHT 1905 

BY 

ORANGE JUDD COMPANY 




^^ 



ALL BIGHTS RESEBVED 



ILLUSTRATIONS 

Plates 

PAGE 

Photograph Showing Soil Physics Laboratory of Iowa 
State College Frontispiece 

Plate 1 — Outfit for Taking Soil Samples 4 

Plate 2 — Apparatus for the Determination of Mois- 
ture 7 

Plate 3 — Apparatus to Test the Effect of Lime on 

Clay Soil 21 

Plate 4 — Compacting Machine for Filling Soil Tubes 25 

Plate 5 — Spring Board Compactor 26 

Plate 6 — Apparatus Used in Exercise 20 32 

Plate 7 — Box in Which Soils Are Exposed in a Sat- 
urated Atmosphere 37 

Plate 8 — Apparatus for the Percolation of Water 

Through Soils 39 

Plate 9 — Aspirator and Frame 41 

Plate 10 — Apparatus for the Study of the Capillary 

Eise of Water 44 

Plate 11 — Apparatus for the Study of the Effect of 

Mulches 48 

Plate 12 — Mechanical Shaker Used in Preparing Soils 

for Mechanical Analysis 67 

Plate 13 — Centrifugal Machine Used in Mechanical 
Analysis of Soils, and Tank for the Supply 
of Distilled Water Under Pressure 69 

Plate 14 — Nest of Sieves Used to Separate Sand Into 

the Various Grades 71 

Plate 15 — Students' Laboratory Desk 74 

Figures 

Figure 1 — The Chromic- Acid Method of Determining 

Organic Matter 56 



CONTENTS 

PAGE 

Exercise 1 — Microscopic Study of Soil Particles. ... 1 

Exercise 2 — Talking Soil Samples 1 

Exercise 3 — Determination of Total Moisture in 

Field Samples of Soils 5 

Exercise 4 — Determination of Capillary Moisture. . . 8 

Exercise 5 — Determination of Hygroscopic Moisture 9 

Exercise 6 — Determination of the Variation in the 

Hygroscopic Moisture of Soils 10 

Exercise 7 — Influence of Cultivation on the Temper- 
ature of the Soil 11 

Exercise 8 — Influence of Evaporation on Soil Tem- 
perature 12 

Exercise 9 — Effect of Eolling upon Soil Temperature 13 

Exercise 10 — Influence of Color on Soil Temperature 14 

Exercise 11 — Influence of Vegetation on Soil Tem- 
perature 15 

Exercise 12 — ^Variation in Soil Temperature at Differ- 
ent Depths 16 

Exercise 13 — Influence of Topography on Soil Tem- 
perature 1 < 

Exercise 14 — The Absorption of Heat by Soils 18 

Exercise 15 — The Effect of Lime upon Clay Soil .... 19 

Exercise 16 — The Elocculation of Clay 21 

Exercise 17 — Determination of the Apparent Specific 

Gravity of Soils 23 



i^ 



viii Contents 

PAGE 

- Exercise 18 — Determination of the Specific Gravity 

of Soils 27 

Exercise 19 — Determination of the Weight of Soil 

per Acre 28 

Exercise 20 — Determination of the Power of Loose 

Soils to Retain Moisture Against Gravity 30 

Exercise 21 — Determination of the Power of Compact 

Soils to Retain Moisture Against Gravity 32 

Exercise 22 — Effect of Humus on the Water-Holding 

Capacity of Soils 33 

Exercise 23— The Power of Air-Dry Soils to Absorb 

Moisture from a Saturated Atmosphere 35 

Exercise 24— Determination of the Rate of Percolation 

of Water Through Soils 38 

Exercise 25 — Rate of Plow of Air Through Soils 40 

Exercise 26— Rate of Rise of Capillary Water in Soils 42 

Exercise 27 — The Amount of Capillary Moisture at 

Different Hights from the Water Table 45 

Exercise 28— The Effect of a Layer of Green or Well- 
Rotted Vegetable Matter upon the Cap- 
illary Rise of Water 46 

Exercise 29— The Effect of Mulches on Evaporation of 

Water from Soils 47 

Exercise 30— Effect of Wetting the Surface of the 
Soil on the Moisture Content of the 
Sub-Soil 49 

Exercise 31 — Determination of Loss on Ignition 60 

Exercise 32— The Effect of Organic Matter on Baking 

of Clay Soils 51 



Contents ix 

PAGE 

Exercise 33 — The Granular Structure of Soils 52 

Exercise 34 — The Effect of Alternate Wetting and 

Drying upon Granulation 53 

Exercise 35 — The Effect of Alternate Freezing and 

Thawing upon Granulation 54 

Exercise 36 — The Effect of Organic Matter on Gran- 
ulation 54 

Exercise 37 — The Chromic-Acid Method of Deter- 
mining Organic Matter 56 

Exercise 38 — Standardization of the Eye-Piece Mi- 
crometer 60 

Exercise 39 — Mechanical Analysis of Soils 62 

Exercise 40 — Mechanical Analysis of Soils by the 

Beaker Method 72 

Appendix 76 

Laboratory Notebook 76 

Precautions to be Observed in Weighing 77 

Weights and Measures, with Equivalents 79 



PREFACE 

Commendable progress has been made during the 
past decade in teaching Soil Physics in the Agricul- 
tural Colleges and High Schools of this country. Up 
to the present time, no comprehensive text book has 
been prepared on this subject. The instructors in the 
various institutions have prepared notes and outlines 
as they have found time and opportunity for this work. 

Without doubt, there is at the present time* a wide- 
spread demand for a text book which covers the various 
phases of the subject. 

In these pages the aim has been to present to the 
instructor and the student a carefully outlined series of 
experiments in Soil Physics. 

This book is the outgrowth of laboratory instruc- 
tion given in the Iowa State College. A portion of 
the experiments outlined in this guide have been used 
quite generally in recent years. Many of them, we 
believe, are now presented for class work for the 
first time. 

An earnest effort has been made to outline the 
exercises briefly and clearly in order that the student 
may proceed with the work without loss of time and 
without confusion. The exercises are also listed in a 
logical order with reference to their relation to each 
other and the skill required on the part of the student. 

It is deemed advisable to assign the exercises which 
call for work in the field either at the beginning of 
the fall semester or toward the close of the spring 
semester. 



xii Preface 

When there are a large number of students in the 
soil laboratory, the work is often facilitated by divid- 
ing the class into groups and assigning a certain num- 
ber of exercises to each group. 

Questions are asked in connection with each 
experiment for the purpose of leading the student to 
a thoughtful study of the data which he has secured. 

The illustrations are original; they are intended 
to show the pieces of apparatus which are new or which 
are not widely distributed. Descriptions of the appa- 
ratus are given for the benefit of instructors who desire 
to equip new soil laboratories or add to their supply 
of apparatus. 

A larger number of exercises are incorporated in 
this guide than can be covered by the student in a term 
of average length; therefore, the work should be ex- 
tended beyond the limits of one term or a portion of 
the exercises should be omitted. 

In the preparation of this guide, the authors have 
drawn upon the publications of the Colleges of Agricul- 
ture and the Experiment Stations of America; upon 
F. H. King's "Physics of Agriculture;" A. D. Hall's 
"The Soil;" Robert Warington's "Physical Properties 
of Soil;" George P. Merrill's "Rocks, Rock-Weathering 
and Soils," and H. W. Wiley's "Agricultural Analysis." 

Iowa State CoUege, Ames, Iowa, 
July, 1905. 

W. H. Stevenson. 

I. 0. SCHAUB. 



Soil Physics Laboratory Guide 1 

EXERCISE 1 

Microscopic Study of Soil Particles 

Object: To study the color, shape, size and 
character of soil particles in different classes of soils. 

Directions : 

1 — Place a few grains of coarse sand upon a glass 
slide and after careful examination with the low power 
of the microscope, make drawings of several of the 
particles and describe them with reference to the 
following points: 

(a) Color — White, grey, brown, red or black. 
(6) Shape — Angular, rounded or irregular. 

(c) Simple or compound. 

(d) Size — Coarse, medium, fine or very fine. 

2 — Study in the same way samples of fine sand, 
loam, loess, clay and peat. 

Questions : 

(a) What factors determine the shape of the 

particles ? 
(&) How do the soils vary? 

1 — In regard to the size of the particles? 
2 — In regard to the simple or complex 

character of the particles? 
3 — In regard to the shape of the particles? 



EXERCISE 2 

Taking Soil Samples 

Object: To acquire skill in taking samples of 
soil for laboratory study. 



2 Soil Physics Laboratory Guide 

Directions : 

Great ^ care should be exercised when samples of 
soil are taken from the field for analysis or study in 
order to secure samples which accurately represent the 
type or types of soil to be studied. 

When samples of soil are taken for laboratory pur- 
poses, the collector must use care in their selection for 
the following reasons: 

1 — "The process of analysis is long, laborious and 
expensive ; and the labor entailed would not be justified 
except in case of samples taken in such a manner as 
to preclude the possibility of a doubt as to their 
typifying the peculiar soils under consideration. 

2 — "The samples used for analysis are very small 
in comparison to the total miass of material to be repre- 
sented by the results of the determination, and a small 
variation of the sample from the true type, when 
multiplied and expressed in terms of the mass, would 
be productive of a great error in results. 

3 — "The soil under consideration is apt to be 
exceedingly variable in composition, making it a most 
difficult operation to secure a sample which shall repre- 
sent any definite area. This is especially true of the 
soils of glacial origin, and the variation may not be 
confined to the surface but is often apparent in samples 
taken at the same depth in different places." 

The method of taking soil samples adopted by 
the Soil Department of the Iowa State College is that 
known as the auger method and is essentially the same 
as that used by the Bureau of Soils of the United 
States Department of Agriculture. 

Samples are sometimes taken with King's Soil 
Tube, but this piece of apparatus is not often used. 

The following directions should be carefully fol- 
lowed in taking soil samples with an auger: 



Soil Physics Laboratory Guide 3 

1-7-Select the spot where the samples are to be 
taken and clean the surface of the ground of grass 
and other vegetation. 

2 — Place the auger over the spot where the sample 
is to be taken; give the auger two or three turns to 
drive it into the soil, but take care not to force it into 
the soil so far that it cannot be readily withdrawn. 
The auger can be withdrawn with greater ease if it 
is given a slight backward turn before an effort is 
made to withdraw it. . 

3 — When the auger has been withdrawn, hold it 
over a piece of oilcloth which is about eighteen inches 
square and release the soil. 

4 — Eepeat this operation until the soil is secured 
to about the depth of the plow line, viz. : five to seven 
inches. Pour the soil from the oilcloth into a canvas 
bag (or air-tight glass jar, if the sample is to be used 
for a moisture determination) and plainly mark each 
receptacle with a label which gives the location where 
the boring was made, character of soil, depth, date and 
any other data which are essential for identification in 
the laboratory. 

5 — Place the auger in the hole thus made, and 
move it up and down the sides several times, without 
turning it, for the purpose of clearing the walls of 
the opening to such an extent that the sub-surface soil 
may be withdrawn without being brought in contact 
with the surface soil. 

6 — Carefully clean out the enlarged hole by sink- 
ing the auger to just the depth reached in taking the 
surface soil; reject the soil which is withdrawn in 
this operation. 

7 — Secure a sample of the sub-surface soil, viz. : 
the soil between the surface soil and the sub-soil, in 
the manner just described for the surface soil; in this 



4 Soil Physics Laboratory Guide 

work, care is required to detect and remove any surface 
soil which may adhere to the outside of the core of 
soil as it is removed. 

8 — Repeat the operation of enlarging and cleaning 
the hole; reject about two inches of the soil between 
the sub-surface and true sub-soil and then secure sam- 
ples of the sub-soil to any desired depth. The sub-soil 
can usually be detected by a marked difference in 
texture and color. 




Plate 1 

OUTFIT FOIl TAIvING SOIL SAMPLES 



The auger is an ordinary wood auger one and one-half 
inches in diameter to which a three-eighth-inch iron gas 



Soil Physics Laboratory Guide 5 

pipe shank has been welded, giving the auger a total 
length of forty inches. This auger can be provided with 
as many additional three-foot lengths of gas pipe as are 
desired. The auger is fitted with a short piece of one- 
half -inch gas pipe for a handle. The attachment is made 
with a T as shown in the illustration. 

A convenient auger for extended trips is one made 
as described above, except that a joint is placed about 
the middle of the shank; this device enables the operator 
to unscrew the auger with a wrench and pack it in a 
suit case. 

The oilcloth is eighteen inches square; it has been 
found to be a very simple and convenient device for 
transferring the soil from the auger to the jars. 

The "King" soil tube is made of brass with steel 
cutting edge and collar and is provided with an eight- 
pound hammer which is shown in the illustration. The 
tube is five feet long; the inside diameter of the cutting 
edge is fourteen-sixteenths of an inch and that of the 
tube one inch. 



EXEEGISE 3 

Determination of Total Moisture in Field 
Samples of Soils 

Object: To compare the total amount of mois- 
ture in soils under the following conditions: 

1 — Sod ground. 
2— Tilled field. 
3 — Summer fallow. 
4 — Fall plowed. 
5 — Stubble. 

Directions : 

1 — Collect quart samples of surface, sub-surface 
and sub-soil to a depth of forty inches ; follow the direc- 
tions outlined in the previous exercise. Secure samples 
representing the above mentioned conditions, within as 



6 Soil Physics Laboratory Guide 

small an area as possible, in order to insure uniformity 
in other soil conditions. 

2 — Determine the total moisture in duplicate for 
the surface, sub-surface and sub-soil, using the corre- 
sponding de|)th of soil from each area. As soon as 
the soil is removed from the auger, it should be placed 
in a self-sealing glass jar or screw-topped brass box 
and properly labeled. Before the vessels are opened 
to take samples for the moisture determinations, the 
contents should be thoroughly mixed by shaking. 

3 — Number and weigh a small sized drying pan 
or evaporating dish and place in it 100 grams of the 
sample to be studied. 

4 — Place immediately in the drying oven and 
keep at 100 to 110 degrees C. for four hours. 

5 — Allow to cool to nearly room temperature and 
weigh. Eepeat the drying and weighing until a con- 
stant weight is obtained. The loss of weight repre- 
sents the total water content of the soil. 

6 — Determine the percentage of moisture com- 
puted on the dry weight of the soil. 

7 — Tabulate the work as follows: 

TOTAL MOISTURE DETERMINATION 



Kind of Pan Wt. Wt. Soil Wt. 1st Wt. 2nd Wt. 3rd Dry Wt. Percent 



Soil 



No. 



Pan 



& Pan 



Dryinti 



Drying 



Drying 



Soil 



Moisture 



Questions : 

(a) Does the surface soil or sub-soil hold the 

larger amount of water? 
(h) Give a list of the soils studied in the order 

of their water holding capacity. 



Soil Physics Laboratory Guide 7 

(c) Discuss the reasons for this difference in 
the water-holding capacity of the various 
soils. 




Plate 2 

APPARATUS FOR THE DETERMINATION OF MOISTURE 



The drying oven is of copper set on a strong iron 
frame. It is ten inches high, ten inches deep and twelve 
inches wide. The oven is provided with a centigrade 
thermometer and has a vent for the escape of moisture. 
Its cost is approximately eight dollars. 

The soil pans are made of tin and are water tight. 
They are 4^x3Vjt inches and 1^2 inches deep. This size 
has been found convenient when the pans are used in the 
oven described above. These pans can be made by any 
tinsmith. 

The scale is known as the "Harvard Trip." It 
weighs accurately to a tenth of a gram and costs 
about eight dollars. 

The jars are quart Mason jars, fitted with good 
rubbers to prevent evaporation. 



8 Soil Physics Laboratory Guide 

EXERCISE 4 

Determination of Capillary Moisture 

Object: To compare the amount of capillary 
moisture in the soils used in the previous exercise. 

Directions : 

1 — Make determinations in duplicate for the vari- 
ous depths of the soils to be studied. 

2 — Carefully weigh the required number of small 
pans or evaporating dishes and place in each 100 
grams of soil. 

3 — Break up all lumps with a glass rod and spread 
out the soil in a thin layer over the bottoms of the 
vessels. Leave the soil exposed to the air at the room 
temperature for twenty-four hours and weigh. 

4 — Expose the soil as above and re-weigh until an 
approximately constant weight is obtained. The loss 
in weight represents the amount of capillary moisture 
in the sample. 

Note — Keep all the samples used in this exercise 
for the determination of hygroscopic moisture. 

5 — Compute the percentage of capillary moisture 
on the basis of water-free soil and tabulate the work 
as follows : 



CAPILLARY MOISTURE 



Kind of 
Soil 



No. 

Pan 



Wt. 

Pan 



Wt. Soil 
&Pan 



Wt. 1st 
Day 



Wt.2nd 
Day 



Wt. 3rd 
Day 



Dry Wt. % Capillary 
Soil Moisture 



Questions : 

(a) What is capillary moisture? 

(b) What is the difference between a water- 
free soil and a soil containing capillary 
moisture ? 



Soil Physics Laboratory Guide 9 

EXERCISE 5 

Determination of Hygroscopic Moisture 

Object: To compare the amount of hygroscopic 
moisture in the soils used in the two previous exercises. 

Directions : 

1 — Use ten-gram samples of the air-dried soils 
used in the previous exercise. 

2 — Heat the required number of clean porcelain 
crucibles with covers in the flame for a short time; 
cool in the desiccator and weigh accurately. 

3 — Place each ten-gram sample of soil in a weighed 
crucible and heat in an air bath at 105 degrees C. for 
two hours. 

.4 — Cool in a desiccator, place cover on crucible 
and weigh as quickly as possible. 

5 — Heat again for an hour, cool and weigh; 
repeat this operation until the weight becomes constant. 

The loss of weight from the air-dried sample 
equals the amount of hygroscopic moisture. 

6 — Determine the percentage of hj^groscopic mois- 
ture on the basis of water-free soil and tabulate the 
work as in the previous exercises. 

Questions : 

(a) What is hygroscopic moisture? 

(h) What is the difference between hygroscopic 
and capillary moisture ? 

(c) Under certain conditions, what water, in 
addition to the two classes referred to 
above, may be included in the total mois- 
ture content of a soil? 



10 Soil Physics Laboratory Guide 

EXERCISE 6 

Determination of the Variation in the Hygro- 
scopic Moisture of Soils 

Object: To compare the amount of hygroscopic 
moisture in sand, loam, silt, clay and peat. 

Directions : 

1 — Determine the hygroscopic moisture in ten 
grams of air-dried samples of sand, loam, silt, clay 
and peat. 

2 — Use duplicate samples and follow the method 
given for the estimation of hygroscopic moisture in the 
preceding exercise. 

3 — Exercise care to weigh out all of the samples 
at the same time to avoid any change in the amount 
of hygroscopic moisture after a portion of the samples 
have been selected, otherwise the comparison will not 
be exact. The amount of heating given the different 
samples should be approximately the same. 

4 — Determine the percentage of hygroscopic mois- 
ture on the basis of water-free soil and tabulate the 
work as in the j)revious exercise. 

Questions : 

(a) What factors determine in a large measure 
the amount of hygroscopic water held by 
each soil? 

(h) Does the organic matter in the soil hold the 
moisture in the same way that it is held by 
the soil particles? 



Soil Physics Laboratory Guide 11 

EXERCISE 7 

Influexce of Cultivatiox ox the Temperature of 

THE Soil 

Object: To show that loose soil is a poor con- 
ductor of heat ; that when the soil is stirred deeply, the 
lower soil receives less heat/ and under certain condi- 
tions remains at a lower temperature than when the 
surface receives shallow cultivation; that the cultivated 
surface soil is warmer than the uncultivated soil. 

Directions : 

1 — For this experiment, prepare three plots as 
follows : 

(a) Compact, uncultivated soil which is free 

from vegetation. 
(h) An adjoining plot cultivated to a depth of 

one and one-half inches. 
(c) Another plot cultivated to a depth of three 
or four inches. 
2 — Take the temperature of the air at four feet 
above the surface of the ground. 

3 — Take the temperature of the soil in each 
plot at a depth of one and one-half, three, six and 
twelve inches below the surface. 

Note — If an unmounted glass thermometer is 
used, open the soil to the desired depth with a small 
pointed iron rod and place the bulb of the thermometer 
at the dei3th at which the temperature is to be taken. 
Leave the thermometer in position about two minutes 
before taking the reading. 

4 — Eecord the temperature for four or more 
different days. The temperature recorded for each 
depth should be the average of at least four readings 
taken a few inches apart. 



12 Soil Physics Laboratory Guide 

5 — Tabulate the data as follows: 





a 
o 

a 






Temperature of Soil 


a> 


Plot A 


PlotB 


Plot C 




1.5 
in. 


3 
in. 


6 
in. 


12 
in. 


I..5 
in. 


3 
in. 


6 
in. 


12 
in. 


15 
in. 


3 
in. 


6 
in. 


12 
in. 




' 




■ 




Mean Temperature 





Questions : 

(a) What are the sources from which the soil 
receives heat? 

(h) What effect does the loose texture of the 
soil have on absorption of heat? On radia- 
tion? On conduction? On evaporation? 
On capillarity? Give the reasons why in 
each case. 

(c) What would be the final effect of all these 
influences on the soil temperature both of 
the surface and the sub-surface, while the 
soil is warming up in the spring? What 
effect in the fall? What do you find? 

(d) What influence has the temperature of the 
soil upon the germination of seeds? 

(e) What can the farmer do in the spring to 
warm up the soil? 



EXERCISE 8 

Influence of Evaporation on Soil Temperature 

Object: To determine the influence of rapid 
evaporation upon the temperature of the soil. 



Soil Physics Laboratory Guide 13 

Directions : 

1 — Prepare two plots as follows: 

(a) A cultivated plot free from vegetation. 
(h) An adjoining plot cultivated and free from 
vegetation to which sufficient water has 
been applied to bring the soil near the satu- 
ration point. The water should be applied 
several hours before the readings are taken. 
2 — Take the temperature of the air at four feet 
above the surface of the ground, and also of the soil in 
each plot at a depth of one and one-half, three and six 
inches below the surface. 

3 — Record the temperature for four or more 
different days and tabulate the data a^ in Exercise 7. 

Questions : 

(a) Why does evaporation lower the temper- 
ature of the soil? 

(b) Why is an undrained soil colder than one 
which is well drained ? 

(c) What is the specific heat of water compared 
with soil? 



EXERCISE 9 

Effect of Rolling Upon Soil Temperature 

Object: To determine the changes in the tem- 
perature of the soil due to rolling. 

Directions : 

1 — For this experiment prepare plots as follows: 
(a) Plot plowed five or six inches deep with 

the surface left loose and open. 
(&) An adjoining plot plowed five or six inches 
deep with the surface rolled. 



14 Soil Physics Laboratory Guide 

2 — Take the temperature of the air at four feet 
above the surface of the ground and also of the soil 
in each plot at a depth of one and one-half, three and 
six inches below the surface. 

3 — Record the temperatures for four or more dif- 
ferent days and tabulate the data as in the preceding 
exercise. 

Questions : 

(a) What is the first effect, of rolling a soil 
which is naturally cold? 

(b) To what is this result due^ 

(c) What influence has rolling upon the evap- 
oration of water from the rolled surface? 

(d) What influence has evaporation upon the 
temperature of the soil? 



EXERCISE 10 

Influence of Color on Soil Temperature 

Object: To determine the difference in the 
temperature of dark and light colored soils. 

Directions : 

1 — Prepare three plots as follows: 

(a) Cultivated plot, free from vegetation. 
(5) An adjoining cultivated plot, the surface 
of which has been blackened with a dressing 
of soot or other black material. 
(c) A third plot, the surface of which has been 
whitened with a dressing of lime. 

2 — Take the temperature of the air at four feet 
above the surface of the ground and also of the soil 



Soil Physics Laboratory Guide 15 

in each plot at a depth of one and one-half, three and 
six inches below the surface. 

3 — Eecord the temperatures every three hours for 
twelve consecutive hours on a clear day and also on a 
cloudy day, and tabulate the data as in Exercise 7. 

Questions : 

(a) Why are dark colored soils higher in tem- 
perature than light colored soils? 

(h) What influence has organic matter upon 
the temperature of the soil? 



EXERCISE 11 

INFLUENCE OF VEGETATION ON SoiL TEMPERATURE 

Object: To determine the difference in the 
temperature between a soil covered with vegetation 
and a bare soil freely exposed to the sky. 

Directions : 

1 — Prepare two plots as follows: 

(a) Plot from which all vegetation has been 

removed. 
(&) An adjoining plot which is covered with a 

heavy grass sod. 

2 — Take the temperature of the air at four feet 
above the surface of the ground and also of the soil 
in each plot at a depth of one and one-half, three and 
six inches below the surface. 

3 — Eecord the temperatures every three hours from 
6 o'clock a. m. to 9 o'clock p. m., on a day when the 
sun is shining and tabulate the data as in Exercise 7. 

Questions : 

(a) Why is the range of temperature of a soil 



16 Soil Physics Laboratory Guide 

shaded by vegetation less than that of a 
bare soil? 

(h) Why is the temperature of the shaded soil 
higher in the early morning than- the 
temperature of the bare soil? 



EXERCISE 12 

Variation in Soil Temperature at Different 

Depths 

Object: To study the daily, weekly and monthly 
variations in soil temperatures to a depth of three feet. 

Directions : 

1 — Place four soil thermometers within a few feet 
of each other, at a depth of six, twelve, twenty-four 
and thirty-six inches respectively, in the soil which is 
to be studied. 

2 — Take the temperature of the air at four feet 
above the surface of the ground, and the reading of 
each thermometer at a given time once each day for a 
period of at least two or three months. 

3 — Tabulate the data as in Exercise 7 and at 
the end of the period of observation plot curves show- 
ing the daily temperature of the air and of the soil 
at the depths mentioned above. 

Questions : 

(a) Is there a point below the surface of the 
soil where the temperature is nearly con- 
stant from day to day? 

(h) Why do the variations in temperature 
diminish with increased depth? 



Soil Physics Laboratory Guide 17 

EXERCISE 13 

Influence of Topography on Soil Temperature 

Object: To determine the influence of the 
degree of inclination of the land surface and the direc- 
tion of the slope upon the temperature of the soil. 

Directions : 

1 — For this experiment, select an area where the 
soil of the same type is found upon an approximately 
level table and upon a slope. 

2 — Take the temperature of the soil on the level 
table and on the slope at a depth of six, twelve and 
twenty-four inches, at a given time once each day for 
a period of at least a week. 

3 — Tabulate the data as follows: 



Topography 


Date 


Hour 


Condition 
of Weather 


Temperature of Soil at 


of Sou 


6 inches 


12 inches 


24 inches 

















Questions : 

(a) When the sun is shining, why is the tem- 
perature of the soil on a south slope 
higher than the temperature of a level 
surface ? 

(h) Why is a southeast aspect generally pre- 
ferred by gardeners? 

(c) Wliy is it preferable to plant corn in rows 
running north and south rather than in 
rows running east and west? 

(d) Why does not vegetation growing upon a 
slope receive increased radiation from the 
sun as does the surface of the ground? 



18 Soil Physics Laboratory Guide 

EXERCISE 14 

The Absorption of Heat by Soils 

Object: To compare the temperature of sand, 
loam, clay and peat at different depths, when these soils 
are exposed to the direct rays of the sun. 

Directions : 

1 — -Provide four zinc or tin boxes about four 
inches wide and eight inches deep, encased in wooden 
covers, except on the top. This cover serves to protect 
the box against all heat exce|)t the direct sunlight on 
the open surface of the soil. 

2 — Fill each of the boxes respectively with sifted 
air-dried sand, loam, clay and peat. 

3 — Take the temperature of the soil in each box 
at a depth of one and one-half, three and six inches 
and then expose the boxes to the direct rays of the 
sun for two hours. 

4 — At the end of this time, take the temperature 
of the air directly above the boxes and also of the soil 
at the depths named above. 

Note — It is a good plan to provide the boxes with 
thermometers set at the different depths. The tem- 
perature of the soils can thus be read off directly. 

5 — Tabulate the data as follows: 





Temp. 
' of 
Air 


Temperature of Soil 
at Beginning 


Temperature of Soil 
After Exposure 


Increase of Soil 
Temperature 


Kind 
of 
Soil 


1.5 in. 


Sin. 


6 in. 


1.5 in. 


Sin. 


6 in. 


1.5 in. 


Sin. 


6 in. 

























Soil Physics Laboratory Guide 19 

6 — Moisten the soil in each box with a given 
amount of water and repeat the experiment as above 
in order to determine the action of moist soil under 
similar conditions. 

Questious : 

(a) What are the factors which influence the 
difl^erence in the absorption of heat by the 
different soils? 

(&) ^Yhat effect has wetting on the absorptive 
power of the soils? Did it affect the 
various soils differently? 



EXERCISE 15 

The Effect of Lime Upon Clay Soil 

Object: To determine the effect of different 
amounts of slacked lime upon the tenacity of clay soil. 

Directions : 

1 — "Weigh out five 100-gram samples of clay soil. 
2 — Add to each sample the amount by weight of 
calcium hydrate (slacked lime) given below: 

No. 1 — None. 

No. 2 — .5 percent. 

No. 3 — 1.0 percent. 

No. 4 — 5.0 percent. 

No. 5 — 10.0 percent. 

3 — Mix each sample thoroughly on a '^mixing 
board" and add just enough distilled water to make 
the soil plastic. 

4 — Mold each sample into the form of a stick by 
compressing the moist clay into a zinc mold which 
is one inch wide and four inches long. First line the 



20 Soil Physics Laboratory Guide 

mold with cheesecloth and compress all of the samples 
to the same degree and then bake in the oven at 110 
degrees C. for four hours. 

• 5 — Eemove the sticks of baked clay from the 
molds and determine the weight required to fracture 
each. 

Note — This determination may be made by 
resting the ends of the stick of clay upon supports 
and suspending from the center a bucket into which 
shot or sand is slowly poured. 

6 — Tabulate the data as follows : 



Sample No. 



Weight Required to Fracture Stick 



Questions : 

(a) How did the lime affect the tenacity of 
the clay? 

(h) What effect does a liberal application of 
lime have upon the physical condition of 
clay soil in the held? 



Soil Physics Laboratory Guide 21 




Plate 3 

APPARATUS TO TEST THE EFFECT OF LIME ON CLAY SOIL 



The molds in whicli the clay is baked are made of 
heavy galvanized iron. They are four and one-quarter 
inches long, one inch wide and three-quarters inch deep. 

As shown in the illustration, retort stands provided 
with iron rings are used for supports and the breaking 
weight is a galvanized iron bucket into which shot or 
sand is poured. 

Care must be exercised in this experiment to mount 
the sticks of clay in such a way that all of them are 
subjected to a uniform strain. 



EXEECISE 16 

The Flocculation of Clay 

Object: To show the effect of calcium hydrate, 
calcium sulphate and sodium chloride in producing 
flocculation of clay. 



22 Soil Physics Laboratory Guide 

Directions : 

1 — Weigh out accurately .2 of a gram of each 
salt; place each sample in a well-cleaned beaker 
and- add 200 c. c. of distilled water. 

2 — Place 200 c. c. of water in another beaker for 
a control. Add to each of the four beakers, one gram 
of clay soil. 

3 — Stir the contents of each beaker thoroughly 
and then put a sample of each in a centrifuge tube 
and whirl in the centrifuge at lowest speed and note 
the time required to completely precipitate each solu- 
tion, that is, to produce a clear solution. 

4 — Thoroughly mix the contents of each centrifuge 
tube and set aside; note the time required for complete 
sedimentation in each case. 

5 — Tabulate the data as follows: 



Solution 



Time to Precipitate 
with Centrifuge 



Time for 
Sedimentation 



Questions : 

(a) Explain the action of the salts in clarifying 
the water. 

(b) Why is a flocculated condition of clay soils 
desirable ? 

(c) What physical effect results from the lim- 
ing of clay soils? 



Soil Physics Laboratory Guide 23 

EXERCISE 17 

Determination of the Apparent Specific Gravity 

OF Soils 

Object: To determine the ratio of unit weight 
to unit volume of different soils. 

Directions : 

1 — Number and weigh carefully eight clean soil 
tubes. 

2 — Fill four of the tubes level full with air- 
dried loesS;, clay, loam and sand, respectively, by pour- 
ing the soils in loosely. Fil] the other four tubes with 
the same soils, using the compacting machine and 
allowing the weight to fall three times from the twelve- 
inch mark upon each measure of soil. 

3 — Weigh the filled tubes carefully. 

4 — Measure the diameter and hidit of the tubes 
and compute the number of cubic centimeters of soil 
contained in each. 

5 — Determine the amount of hygroscopic water 
in a sample of each of the soils taken when the tubes 
are filled. 

6 — Calculate the apparent specific gravity of the 
different soils. (Apparent Specific Gravity equals 
weight of 1 c. c. of soil divided by weight of 1 c. c. 
of water.) 

7 — Tabulate the data as follows and calculate the 
weight of an acre of the different soils to a depth of 
one foot. 



24 Soil Physics Laboratory Guide 



Kind 

of 

Soil 


No. 

of 

Tube 


Wt. 

of 

Tube 


"Wt. of 
Tube 

&Soil 


Vol. of 
Tube 


Amt. 

Hy. 

Water 


Net 

Wt. of 

Soil 


Wt. of 

1 c.c. 

Soil 


A pp. 
Sp. Gr. 
of Soil 


Wt. of 

Acre of 

Soil in 

. Tons 























Questions : 

(a) Which is heavier, a coarse or fine grained- 
soil ? Why ? 

(h) What influence has the presence of stones 
upon the apparent specific gravity of a soil ? 

(c) What influence has plowing upon the ap- 
j)arent specific gravity of a soil? 



Soil Physics Laboratory Guide 25 




Plate 4 
COMPACTING MACHINE FOR FILLING SOIL TUBES 



The compacting machine shown in the illustration 
was designed to pack the soil into the tubes more 
uniformly than can be done by hand. The latter 
method, even when great care is exercised, gives very 
unsatisfactory results. 

The illustration shows the construction of the com- 
pactor; the table is two feet wide, three feet long and 
three feet high; the wooden posts in front are six inches 
square. The iron shaft which carries the plunger and 
weight is one inch in diameter; the plunger is two inches 
in diameter; the weight is four inches long and two 
inches in diameter; the weight strikes upon a support 
which is attached to the shaft by a set screw. 



26 Soil Physics Laboratory Guide 

The adjustment of the tube, phinger and weignt.is 
shown. The weight may be dropped any number of times 
from a given hight. The soil tubes which are shown on 
the compactor and which are used in Exercise 17, are 
made of galvanized iron with solid bottoms. These -tubes 
are twelve inches long and two inches inside diameter. 

A better grade of tubes are made of brass, but very 
satisfactory results are secured with the cheaper galvan- 
ized iron tubes. 




Plate 5 



SPRING BOARD COMPACTOR 



The spring board compactor is a cheap but a very 
satisfactory compacting machine. It may be used in- 
stead of the larger and more expensive compactor shown 
in Plate 4. 

This piece of apparatus is made of one-inch pine 
boards, four feet long and eight inches wide. A two by 
four-inch block is placed between the boards, six inches 
from the right end. The boards are securely nailed to 
this block and are also fastened together by two half-inch 
bolts. Another block about an inch and a half in thick- 



Soil Physics Laboratory Guide 27 

ness is nailed to the lower board ten or twelve inches 
from the left end. 

The wooden upright in the center is securely 
fastened to the lower board and passes loosely through 
an opening in the upper board. An iron weight of two 
and one-half kilos is dropped upon the board from a 
hight of twelve or eighteen inches. The tube which con- 
tains the soil which is to be compacted is supported by 
rings as shown in the illustration. The tube is filled 
with soil and the entire depth compacted at one operation. 



EXERCISE 18 

Determination" of the Specific Gravity of Soils 

Object: To compare the weights of different 
soils with the weights of equal volumes of distilled 
water. 

Directions : 

1 — Fill a specific gravity flask carefully with dis- 
tilled water which has been previously boiled for a few 
minutes and allowed to cool to the room temperature, 
which is recorded. Have the capillary stopper just 
filled with water. Wipe the flask perfectly dry and 
weigh. 

2 — Pour out about one-third of the water and 
place in the flask about ten grams of accurately weighed 
sand which has been dried to a constant weight at 
110 degrees C. 

3 — Heat the flask for a few minutes on the water 
bath, until the air is expelled. Eemove the flask and 
cool to the first temperature, and fill with previously 
boiled and cooled water; dry and weigh at the original 
temperature. 

4 — With the same method determine the specific 
gravity of loam, loess, clay and peat. 



28 Soil Physics Laboratory Guide 

5 — Calculate the specific gravity (weight of soil 
divided by weight of water displaced by soil), and 
tabulate the results as follows: 

SPECIFIC GRAVITY OF SOILS 



Kind of 
Soil 



Wt. of Flask Filled 
with Water 



Wt. of Soil 



Wt. of Flask 
and Soil 



Specific Gravity 



G — From the data in Exercises 17 and 18, 
determine the percent of porosity, i. e., the space which 
in the dry soil is occupied by the air, of the different 
soils which were used. 

Questions : 

(a) Why is it necessary to use water-free soil? 

(&) Why does the sand have a higher specific 

gravity than the clay, loam and peat? 

(c) How does the amount of humus in the soil 
influence its specific gravity? 

(d) Why is it necessary to Aveigh the flask each 
time at the same temperature? 



EXERCISE 19 

Determination of the Weight of Soil Per Acre 

Object: To determine the weight of dry soil to 
a given depth per acre. 

Directions : 

1 — Drive into the soil a brass tube (eight inches 
long and about three inches in diameter, sharpened 



Soil Physics Laboratory Guide 29 

at its lower edge) until the top is level with the 
surface. 

2 — Dig away the soil around the tube; empty the 
tube upon a piece of oilcloth and transfer the soil to 
a Mason jar; carefully drive the tube down again and 
thus obtain a sample of the succeeding eight inches. 
Repeat this operation until eight-inch samples of the 
soil have been secured to any desired depth. 

3 — Carefully weigh each sample. 

4 — Determine the total moisture in 100 grams 
of soil from each depth and from these data determine 
the dry weight. 

5 — Calculate in cubic inches the contents of the 
tube. 

6 — Calculate the weight of an acre of soil to the 
depth at which each sample was taken and tabulate the 
results as follows: 



Kind of 
Soil 



Depth of 
Sample 



Cubic Inches 
of Soil 



Weight of 
SoU 



Percent of 
Moisture 



Dry Weight 
of Soil 



Wt. of Dry 
Soil per Acre 



Question : 

(a) Why does a soil gradually increase in 
weight as we go into the sub-soil? 



30 Soil Physics Laboratory Guide 

EXERCISE 20 

Determination of the Power of Loose Soils to 
Eetain Moisture Against Gravity 

Object': To compare the power of various types 
of loose soil to hold water against gravity. 

Directions : 

1 — Place a disc of cheesecloth in the bottom of 
a perforated tube, moisten the cloth and weigh care- 
fully. 

2 — Fill the tube with loose sand, exercising care 
not to compact the soil, and weigh the filled tube. 

3 — Stand the tube in a vessel containing water 
to a hight nearly equal to that of the surface of the 
soil. Leave the tube standing in this position until 
the surface of the soil becomes thoroughly moistened. 

4 — Eemove the tube from the water, wipe dry, 
place in a small pan and weigh. 

5 — Cover the tube with a glass plate and set it 
where the water will drain away. Weigh the tube at 
the end of the first hour, second hour, and daily there- 
after for five days. 

6 — Determine the hygroscopic moisture in a sep- 
arate sample at the time of filling the tube. 

7 — Calculate on a water-free basis, the percent 
of water held by the sand. 

8 — In the same way determine the percent of 
water held by loam, clay, loess and peat. 



Soil Physics Laboratory Guide 31 

9 — Tabulate the data as follows: 



Kind of 
Soil 



Weight of 
Tube 



Weight of 
Tube and Soil 



Weight of 
Soil 



Percent of 

Hygroscopic 

Moisture 



Weight of 
Dry Soil 



Weight of Tube 


Weight of Tube and Soil at 


and Saturated Soil 


1 hr. 


2 hrs. 20 hrs. 


50 lire. 


74 hrs. 


98 hrs. 

















Weight of Water Retained 


Percent o| Water Retained 


Hours 


Hours 


Saturated 


1 


2 


26 


50 


74 


98 


Saturated 


1 


2 


26 


50 


74 


98 































Questions : 

(a) What is a saturated soil? 

(h) Which type of soil loses water most rapidly 

at first? Which percolates for the longest 

time? 
(c) Calculate the total number of pounds of 

water retained per cubic foot of dry soil 

and also the number of inches of rainfall 

which it re]3resents? 



32 Soil Physics Laboratory Guide 




Plate 6 



APPAEATUS USED IN EXERCISE 20 



A four-gallon jar is a convenient vessel to use in 
this exercise. 

The soil tubes which are used to determine the power 
of soils to retain water are made of galvanized iron. 
They are twelve inches long and two inches inside diame- 
ter. The bottoms are set up one inch from the lower 
end and are perforated as shown in the illustration. 

These tubes can be made of brass if tubes of a better 
quality are desired. 



EXERCISE 21 

Determination of the Power of Compact Soils to 
Retain Moisture Against Gravity 

Object: To compare the power of various types 
of compact soils to hold water against gravity. 



Soil Physics Laboratory Guide 33 

Directions : 

1 — Proceed with this experiment as in the previous 
exercise, except that the tubes are to be filled as follows : 

Use the soil compacting machine, allowing the 
weight to fall three times from the twelve-inch mark 
upon each measure of soil. 

2 — Calculate on a water-free basis, the percent 
of water held by the compact soils and tabulate the 
data as in the preceding exercise. 

Questions : 

(a) What conclusions do you draw from these 
data, regarding the effect of rolling upon 
the water-holding capacity of the soil? 

(&) What effect has cultivation upon the 
water-holding capacity of the soil? 

(c) What type of soil has its water-holding 
capacity changed to the greatest extent by 
compacting. 



EXERCISE 22 

Effect of Humus on the Water-Holding Capacity 

OF Soils 

Object : To determine the effect of different 
amounts of humus upon the water-holding capacity of 
various types of soil. 

Directions : 

1 — Place a disc of cheesecloth in the bottom of the 
required number of perforated soil tubes. 
2 — Prepare the following samples: 

No. 1 — 600 grams of sand. 

No. 2 — 570 grams of sand and 30 grams of peat. 



34 Soil Physics Laboratory Guide 

No. 3 — 540 grams of sand and 60 grams of peat. 
No. 4 — 480 grams of sand and 120 grams of peat. 
No. 5 — Number of grams of peat required to fill 
the tube to the same hight as the other 
tubes. 
Thoroughly mix each of these samples on a "mix- 
ing board^^ and fill the tubes, which have been num- 
bered to correspond with the samples, by using the soil 
compacting machine, allowing the weight to fall three 
times from the twelve-inch mark upon each measure 
of soil. 

3 — Stand the tubes in a vessel containing about 

four inches of water and allow them to remain in the 

water until the weight becomes approximately constant. 

4 — Remove the tubes from the water, place each 

in a small pan to catch the possible drainage and weigh. 

5 — Eepeat the experiment with clay and loess. 

6 — Determine the percentage of water retained by 

each sample and tabulate the data as follows: 



Sample No. 


Weight of Tube 
and Soil 


Weight of Tube, Soil 
and Water Held 


Percent of Water 
Held 











Questions : 

(a) Compare the amount of water held by the 
mixtures with the amount held by equal 
weights of the sand and peat when tested 
separately. 

(h) Basing your calculations on the data ob- 
tained, determine the additional amount of 



Soil Physics Laboratory Guide 35 

water which an application of eight tons of 
peat will enable an acre of soil to hold to 
a depth of five inches, 
(c) Why does humus increase the water-holding 
capacity of a soil? 



EXERCISE 23 

The Power of Air-Dry Soils to Absorb Moisture 
FROM A Saturated x\tmosphere 

Object: To determine the total amount of 
moisture ^ absorbed from a saturated atmosphere by 
different types of air-dry soil. 

Directions : 

1 — Place 400 grams of air-dry loam in an accu- 
rately weighed soil pan; weigh also one empty soil pan 
to serve as a check. 

2 — Place the pans on a shelf in a tightly covered 
vessel which contains a saturated atmosphere. Record 
the temperature of the air in the vessel at each weighing. 

3 — After twenty-four hours, weigh each pan and 
deduct the increase in weight of the empty pan from 
the increase in weight of the pan containing the sample. 

4 — Eepeat the weighings every twenty-four hours 
until, with the same conditions of temperature, an 
approximately constant weight is obtained. Weigh the 
pans as rapidly as possible to prevent loss of moisture 
by evaporation. 

5 — Determine the hygroscopic moisture of the loam 
with a special sample at the time of placing the soil 
in the pan. 

6 — Calculate the amount of water absorbed by 
100 grams of the air-dry loam and the total amount 



36 Soil Physics Laboratory Guide 

of water taken from the air by 100 grams of water- 
free soil. 

7 — Determine in the same way the amount of water 
absorbed from the air by sand, clay and peat and 
tabulate the data as follows : 



Kind of 


Wt. of Pan 
and Soil 


Wt. of 

Hygroscopic 
Moisture 


Weight of Pan 
and Soil 


Percent of 
Moisture Ab- 
sorbed by Air- 
dried Soil 


Total Per- 
cent of 


Soil 


24 hrs. 


48 hrs. 


72 hrs. 


Moisture in 
Sou 













Questions : 

(a) Which class of soils absorbs the largest 
amount of moisture from the air? Why? 

(&) How does the amount of water which a 
soil is capable of absorbing from the air 
compare with the moisture content of the 
soil when growing corn plants wilt? 



Soil Physics Laboratory Guide 37 




Plate 7 

BOX IN WHICH SOILS ARE EXPOSED IN A SATURATED 
ATMOSPHERE 



This box is made of zinc. It is twenty-six inches 
long, fourteen inches wide and six inches deep and is 
provided with a closely fitting cover. 

There are two tiers of strips the full length of the 
vessel on which rest the soil pans. Openings are cut in 
these strips in which pieces of blotting paper are fitted. 
The ends of the paper extend into the water, which is 
kept not less than an inch deep in the bottom of the 
vessel. 

The soil pans used in this exercise are made of tin 
and are six and one-half by six and one-half inches and 
one and five-eighths inches in depth. 



38 Soil Physics Laboratory Guide 

EXERCISE 24 

Determination of the Eate of Percolation of 
Water Through Soils 

Object: To compare the rate of percolatioli of 
water through soils of different texture. 

Directions : 

1 — Use in this experiment sand, clay and loam. 

2 — Fill, without compacting, within an inch of the 
overflow pipes, each of the soil tubes provided for this 
experiment, with one of the soils named above, and 
place a half-inch layer of gravel on the surface to 
prevent disturbance of the soil by the flowing water. 

3 — Connect the filled tubes with short pieces of 
rubber tubing, by means of the lateral inlets, and close 
with corks the openings at the extreme ends of the 
series. 

4 — Pour in water gently in quantities sufficient to 
keep the tubes almost level full and maintain the same 
water level in each tube. 

5 — Note the time until percolation begins from 
the drainage tubes, then place an Erlenmeyer flask 
beneath each. When the flow becomes constant, collect 
the water which percolates through the soil in thirty 
minutes and measure carefully. 

6 — Determine in the same way the amount of 
water which percolates in thirty minutes through 
compacted sand, clay and loam. 



Soil Physics Laboratory Guide 

7 — Tabulate the results as follows: 



39 





Loose 


Compact 


Kind of Soil 


Time for 
Percolation 


c. c. Water Perco- 
lated in 30 Min 


Time for 
Percolation 


c. c. Water Perco- 
lated in 30 Min. 













Questions : 

(a) Why does the water percolate most rapidly 
through the soil which has the least total 
pore space? 

(&) What factors, other than texture, facilitate 
the percolation of water through loam and 
clay soils under natural field conditions? 




Plate 8 

APPARATUS FOR THE PERCOLATION OF WATER THROUGH SOILS 



The soil tubes used in this exercise are made of 
galvanized iron. They are eighteen inches long and two 



40 Soil Physics Laboratory Guide 

inches in diameter, with soh'd bottoms. The lateral inlets 
are three-eighth-inch tubes, one inch long; they are 
placed one and one-half inches below the top of the soil 
tubes. The drain pipe is one-quarter inch in diameter, 
two and one-half inches long, and is three-quarters of an 
inch above the bottom of the tube. 

The block which is used to support the tubes is three 
by three inches. The holes are two and one-quarter 
inches in diameter, two inches deep, and are five inches 
from center to center. 

Notches are cut in the side of the block to accom- 
modate the drain pipes. This block can be used also in 
other exercises. 



EXEKCISE 25 

Eate of Flow of Air Through Soils 

Object: To compare the rate of the flow of air 
through soils of different texture. 

Directions : 

1 — For this experiment use sand, loam, clay and 
loess. 

2 — Fill the required number of soil tubes pro- 
vided for this experiment with the above named soils. 
Use the compacting machine as directed in previous 
exercises. 

3 — Connect the soil tubes successively to the cock 
on the aspirator with rubber tubing and note the num- 
ber of degrees passed by the pointer in a given time. 

4 — Determine the rate of flow per hour for the 
different soils and tabulate the data as follows: 



Kind of Soil 


Degrees Passed by Pointer 
in Specified Time 


Rate of Flow per Hour 









Soil Physics Laboratory Guide 41 



Questions : 

(a) What relation does the aeration of the soil 
sustain to the action of bacteria in the soil ? 

(b) Do the different soils sustain the same rela- 
tion to each other in regard to the rate of 
the flow of air that is sustained in the 
percolation of water? 




Plate 9 



ASPIRATOR AND FRAME 



The base of the frame is four feet long, twelve 
inches wide and two inches thick. The uprights and 
cross-bar are made of two by two-inch material. The 
total hight is three feet ten inches. 



42 Soil Physics Laboratory Guide 

The outside can, which holds the water, is eighteen 
inches high and nine and one-quarter inches in diameter. 
The inside can is eighteen inches higii and eight and one- 
half inches in diameter. It is fitted with a ring and cock 
as shown in the illustration. 

■ The larger can is nearly filled with water; the sjnaller 
can is pushed down into the water with the cock open 
to permit the air to escape. The cock is then closed and 
the tube containing the soil is attached to the cock of 
the aspirator by means of a piece of rubber tubing which 
is long enough to extend to the top of the frame. 

The weight is about twice as heavy as the can to 
which it is attached with window cord. The cord passes 
through a pulley near the end of the frame which is 
similar to the one shown in the illustration, except that 
the axle passes through the dial and carries a pointer. 
To operate the aspirator, open the cock and start the 
weight from the same point each time. 

The soil tubes are made of galvanized iron. They 
are eighteen inches long and two inches in diameter. 
The tube near the bottom is one-fourth of an inch in 
diameter, two inches long and is curved upward as shown. 
The block in which the tubes are supported is similar to 
the one used in the previous exercise. 



EXERCISE 26 

Rate of Rise of Capillary Water in Soils 

Object: To compare the rate of the rise of 
capillary water in soils of different texture. 

Directions : 

1 — For this experiment use coarse sand, fine sand, 
loam, clay, loess and peat. 

2 — Select twelve o^lass tubes, one inch in diameter, 
of uniform bore, and close one end of each by means of 
a piece of cheesecloth, firmly tied on. 

3 — Fill six of the tubes with the finely pulverized 



Soil Physics Laboratory Guide 43 

air-dried soils, pouring the soil in loosely, care being 
taken not to compact it. Fill the remaining six tubes 
by .compacting the soil by gently tapping the tubes 
during the time of filling. 

4 — Place the tubes in a wooden frame in such a 
manner that the lower ends are immersed in about an 
inch of water. 



5 — Make readings at the following intervals: 
1 hour, 2 hours, 3 hours, 6 hours, 9 hours, 12 hours, 
18 hours, 24 hours, 36 hours, 48 hours, and daily there- 
after until no further rise is noted. Note the total 
hight to which the water has risen and the rise in the 
water column since the previous reading. 

6 — Tabulate the data as follows: 





Hight of Water in Inches 




Kind of Soil 


1 


2 


3 


o 


9 


12 


18 


24 


36 


48 


72 


Hours 


Loose 













Compact 


« 



Questions : 

(a) What factors influence the capillary rise of 

water in soils? 
(h) Does the water rise to the greatest hight in 

the soil in which the rise is most rapid at 

first? 



44 Soil Physics Laboratory Guide 




Plate 10 
APPARATUS FOR THE STUDY OF THE CAPILLARY RISE OF WATER 



The frame in which the glass tubes are supported is 
two and one-half feet wide and four feet high. It is 
made of material one inch thick and four inches wide. 
The frame rests upon two blocks, sixteen inches long. 
The holes in the upper cross-bar, which receive the glass 
tubes, are flush with the edge and the tubes are held in 
position by wooden buttons as shown. 



Soil Physics Laboratory Guide 45 

EXERCISE 27 

The Amount of Capillary Moisture at Different 
HiGHTs FROM the Water Table 

Object : To determine the amount of capillary 
moisture held at different hights from the water table 
by soils of different texture. 

Directions : 

1 — Use the same soils which were used in the 
preceding exercise. 

2 — Fill six sectional brass soil tubes, five feet in 
length, over the lower ends of which pieces of cheese- 
cloth have been firmly tied, with the finely pulverized 
air-dried soils, pouring the soil in loosely, care being 
taken not to compact it. Fill six other tubes by com- 
pacting the soil by tapping the tubes gently. 

3 — Place the tubes in a frame with the lower ends 
standing in about one inch of water. 

4 — At the end of thirty days, separate the one-foot 
sections from each other and determine the percent of 
moisture held in each successive foot above the water 
table. For the moisture determination use about a 100- 
gram sample of the soil taken from the top of each 
section. 

5 — Tabulate the data as follows: 







Percent of Moisture 




Loose 


Compact 


Kind of Soil 




2 ft. 


.•}ft. 


4 ft. 


5 ft. 


1ft. 


2 ft. 


3 ft. 


4 ft. 


5 ft. 







46 Soil Physics Laboratory Guide 

Question : 

(«) Why is there a difference in the percent of 
water held at the different hights from the 
water table? 



EXERCISE 28 

The Effect of a Layer of Green or Well-Eotted 

Vegetable Matter Upon the Capillary Eise 

OF Water 

Object: To determine the extent to which a 
layer of vegetable matter breaks the capillary rise of 
water in soils. 

Directions : 

1 — Select three glass . tubes about two feet long 
and two inches in diameter, of uniform bore, and close 
one end of each by means of a piece of cheesecloth 
firmly tied on. 

2 — Fill one tube with finely pulverized air-dried 
loam, pouring the soil in loosely. Fill a second tube 
with the same soil to a depth of one foot; then place 
in the tube a two-inch layer of coarsely cut green 
material and complete the filling of the tube with the 
loam. Fill the third tube in the same way except that 
well-rotted manure is to be substituted for the green 
material. 

3 — Place the tubes in a frame with the lower ends 
standing in about one inch of water. 

4 — Observe the rise of the capillary water in each 
tube and report in narrative form your observations, 
which should extend over one week. 
Question : 
(a) What is the practical lesson taught by this 
experiment ? 



Soil Physics Laboratory Guide 47 

EXERCISE 29 

The Effect of Mulches on Evaporation of Water 

FROM Soils 

Object: To determine the amount of evapora- 
tion which takes place from soils when they are culti- 
vated at different depths and when they are mulched 
with various materials. 

Directions : 

1 — Fill the required number of soil cylinders 
provided for this experiment with fine air-dried loam, 
compacting the soil uniformly and filling the cylinders 
to the same level. 

2 — Treat the soils in the different cylinders as 
follows : 

Xo. 1 — No treatment. 

N'o. 2 — Cultivated one inch deep. 

No. 3 — Cultivated three inches deep. 

No. 4 — Cultivated five inches deep. 

No. 5 — Mulched with two inches of leaves. 

No. 6 — Mulched with two inches of cut straw. 

3 — ^Cultivate the soil each day by thoroughly 
stirring the surface to the required depth. 

4 — Fill the water supply tubes on the cylinders 
with water to the same level every day, and after evap- 
oration begins, keep a careful record for one week of 
the amount of water given off every twenty-four hours. 
Cover the supply tubes with corks or glass plates in 
order to prevent evaporation from the water surface. 

5 — Determine the surface area of the cylinders 
and compute the number of tons of water evaporated 
per acre during a period of one week. 

6 — Eepeat this experiment with a sandy soil. 



48 Soil Physics Laboratory Guide 

7 — Tabulate the data as follows: 



Number 

of 
Cylinder 



Number of c. C Water Evaporated 



Ist day 2d day 3d day 



4th day 



5th day 



6th day 



'th day 



Total No. 
c. c. Water 



Tons per 
Acre 



Questions : 

(a) What is the effect of a mulch? 

(&) Which method of cultivation conserves the 

greatest amount of moisture? 
(c) Is the amount of water evaporated from 

day to day the same? If not, why? 




Plate 11 

APPARATUS FOR THE STUDY OF THE EFFECT OF MULCHES 



The cylinders are made of galvanized iron. They 
are eleven inches in diameter and thirteen inches high. 



Soil Physics Laboratory Guide 49 

The water supply tubes are one inch in diameter. Cylin- 
ders of this style permit evaporation to take place from 
quite a large area. 

EXERCISE 30 

Effect of Wettin"g the Surface of the Soil on" 
THE Moisture Content of the Sub-Soil 

Object: To stud}^ the translocation of water 
occasioned by wetting the surface of the soil. 

Directions : 

1 — Select a plot of fallow ground eight feet 
square and make moisture determinations with samples 
taken in six-inch sections down to a depth of three feet. 
Each sample should be made up of soil from several 
borings. 

2 — Add to the plot slowly with a sprinkler, 128 
pounds of water. 

3 — Twenty-four hours after applying the water, 
take composite samples near the points at which the 
first samples were taken and determine the amount of 
water in each. Also take samples a few feet from the 
wet area and determine the moisture content. 

4 — Make moisture determinations in the same way 
forty-eight hours after applying the water. 

5 — Tabulate the data as follows : 





Wet Area 


Area Not Wet 


Depth 

of 
Samples 


Percent of Water 


Percent of Water 


Before 

Wetting 


24 hia. After 
Wetting 


48 hrs. After 
"Wetting 


24 hrs. 


48 hrs. 










' 





50 Soil Physics Laboratory Guide 

Questions : 

(a) What effect may a light rain in summer 
have upon the water content in some of the 
lower strata? 

(h) In dry weather is it advisable to simply 
wet the surface around a recently planted 
tree? If not, why? 

(c) Why is it advisable to practice shallow 
cultivation as soon after a considerable rain- 
fall as the implements will work satis- 
factorily ? 



EXERCISE 31 

Determination of Loss on Ignition 

Object: To determine the loss on ignition due 
to the removal of water in combination with certain 
materials, all organic acids and ammoniacal com- 
pounds, all organic matter and the carbon dioxide in 
carbonates. 

Directions : 

(Method of the Official iigricultural Chemists.) 

1 — Place five grams of the water-free soil in a 
weighed crucible and heat to low redness. 

2 — Stir the soil occasionally and continue the heat- 
ing until all organic material is burned away, but below 
the temperature at which alkaline chlorides volatilize. 

3 — Moisten the cold mass with a few drops of a 
saturated solution of ammonium carbonate, dry and 
heat to 150 degrees C. to expel excess of ammonia. 
The loss in weight of the sample represents organic 
matter, water of combination, salts of ammonia, etc. 



Soil Physics Laboratory Guide 51 

4 — Determine by this method the loss on ignition, 
of the following soils : sand, loam, clay, loess and peat. 

Tabulate the data as follows: 



Kind of Soil 



No. of 
Crucible 


Wt. Crucible 
and Soil Be- 
fore Heating 


Wt. Crucible 

and Soil 
After Heating 


Loss on 
Ignition 











Percent 
of Loss 



Questions : 

(a) Does the soil change color on ignition? 

Why ? 
(5) Why is there a greater loss on ignition with 

loam than with sand? 



EXERCISE 32 

The Effect of Organic Matter on Baking of 
Clay Soils 

Object : To show the degree to which organic 
matter prevents the baking of clay soils. 

Directions : 

1 — Secure four one-gallon jars provided with drain- 
age outlets and fill them to within one inch of the top 
as follows : 

No. 1— Clay. 

No. 2 — Clay thoroughly mixed with five per- 
cent of peat by weight. 

No. 3 — Clay thoroughly mixed with ten per- 
cent of peat by weight. 



52 Soil Physics Laboratory Guide 

No. 4 — Cla}^ thoroughly mixed with twenty per- 
cent of peat by weight. 
2 — Apply enough water to saturate the soil, using 
the same amount of water in each case, and expose the 
jars to the direct rays of the sun until the soil is baked. 
3 — Examine the soils and determine the ease with 
which the baked surface can be pulverized with the 
fingers. 

4 — Eecord your observations in narrative form in 
your note book. 

Questions : 

(a) What causes a clay soil to bake? 
(h) In what way does the crust formed by the 
baking injure the growing plant? 

(c) How does organic matter tend to prevent 
the "running together'^ or baking of soils? 

(d) What can the farmer do to prevent the 
baking of the soil? 



EXERCISE 33 

The Granular Structure of Soils 

Object: To compare the granular structure of 
surface, sub-surface and sub-soils. 

Directions : 

1 — Secure samples of the surface, sub-surface and 
sub-soil of loam without destroying the granular 
structure. 

2 — Examine a small portion of each sample with 
the microscope; make drawing showing the granular 
structure and note the shape and size of the granules. 



Soil Physics Laboratory Guide 53 

3 — Place about ten grams of each sample in a 
shaker bottle with 75 c. c. of distilled water and shake 
for fifteen hours. 

4 — Again examine each sample with the micro- 
scope and note the difference in the size and structure 
of the particles. 

Questions : 

(a) What factors cause a difference in the 
granular structure of a soil at different 
depths ? 

(h) Why is granulation a desirable property 
of soils? 



EXERCISE 34 

The Effect of Alternate Wetting and Drying 
Upon Granulation 

Object: To study the effect of alternate wetting 
and drying upon the granulation of a loam soil rich in 
organic matter and a clay soil deficient in organic 
matter. 

Directions : 

1 — Mix 400 grams of each of the soils with water 
and completely puddle by working on the "mixing 
board/' 

2 — Mold each sample into a large ball; place the 
balls on a board or cloth and thoroughly dry by expos- 
ing to the rays of the sun or heating in the oven at 
about forty degrees C. 

3 — Again moisten the mass and dry as before. 
Eepeat the operation two additional times. 

4 — Examine the soils after each period of drying 
and describe in narrative form what has taken place. 



54 Soil Physics Laboratory Guide 

EXERCISE 35 

The Effect of Alternate Freezing and Thawing 
Upon Granulation 

Object: To study the effect of alternate freezing 
and thawing upon the granulation of a loam soil rich 
in organic matter and a clay soil deficient in organic 
matter. 

Directions : 

1 — Mix 400 grams of each of the soils with water 
and completely puddle by working on the "mixing 
board." 

2 — Mold each sample into a large ball; place the 
balls on a board or cloth and expose in a freezing 
temperature until the soil is frozen solid. 

Note — In freezing weather the balls may be ex- 
posed out of doors; at other times, if a cold storage 
room is not at hand the balls may be placed in a 
covered can and packed in ice and salt after the manner 
of an ice cream freezer. 

3 — Next thaw out the soils by exposing the balls 
at the temperature of the laboratory. 

4 — Repeat this alternate freezing and thawing 
three additional times. 

5 — Examine the soils after each period of thawing 
and describe in narrative form what has taken place. 



EXERCISE 36 

The Effect of Organic Matter on Granulation 

Object: To study the effect of organic matter 
upon the granulation of a soil rich in that material. 



Soil Physics Laboratory Guide 55 

Directions : 

1 — Secure a loam soil which is rich in organic 
matter. 

2 — Wet about 300 grams of the soil and thor- 
oughly puddle by working on the "mixing board." 
Then mold the soil into a large ball. 

3 — Place another 300-gram sample in a percolator 
and leach out the soluble salts with a one percent 
solution of hydrochloric acid. Wash the soil free of 
acid, puddle and mold into a ball. 

4 — Extract the soluble salts from another 300- 
gram sample of soil; wash free from acid and transfer 
the soil to a four-liter bottle. Nearly fill the bottle 
with a four percent solution of ammonia and shake 
occasionally for twenty-four hours in order to extract 
a portion of the humus. Decant the ammonia solution 
into a vessel and set aside. Wash the soil free from 
ammonia and mold into a ball. 

5 — Freeze and thaw the three balls four times in 
the manner described in the preceding exercise. 

6 — Note the appearance of the balls after each 
period of thawing. 

7 — Evaporate the ammonia solution which was 
used in extracting the humus from ball No. 3 nearly 
to dryness on the water bath. 

8 — Mix the residue left after the evaporation, with 
the soil from which it was removed. Mold the mass 
into a ball and freeze and thaw four times. 

9 — Compare the condition of this ball after each 
thawing with the condition of the other balls. 

Questions : 
(a) Why is the soil in better condition for 

cultivation after a cold winter? 
{&) What influence has organic matter on 
granulation ? 



56 Soil Physics Laboratory Guide 

EXERCISE 37 

The Chromic-Acid Method of Determining 
Organic Matter 




Fig. 1 

THE description OF THIS METHOD IS TAKEN FROM 

BULLETIN NO. 34, BUREAU OF SOILS 



The combustion is effected in a round-bottomed 
flask F, Fig. 1, of about 400 c. c. capacity, fitted with 
a three-hole rubber stopper. The stopper is fitted with 
a dropping funnel, a tube for the introduction of air 
previously freed from carbon dioxide by bubbling 
through a solution of potassium hydrate in the flask G, 
and a tube leading through a condenser to a train of 
absorption bulbs. This train contains first, a Peligot 
tube A, containing a saturated and slightly acidified 
solution of silver sulphate to absorb both hydrochloric 
acid and sulphur trioxide or dioxide should they be 
generated; then a guard tube B, containing concen- 
trated sulphuric acid, followed by a potash bulb C, 
and an acid bulb D, to be weighed with the potash 
bulb. An acid guard bulb E, completes the train. 
The whole apparatus is attached to an aspirator so that 



Soil Physics Laboratory Guide 57 

air free from carbon dioxide can be drawn throiigli the 
combustion flask and train. The procedure is as 
follows : 

"A sample of the soil, usually about ten grams, 
is carefully weighed and brought into the combustion 
flask. If the sample be rich in organic matter, it has 
been found advisable to introduce also some sand, 
previously ignited before the blast, and in an amount 
dependent roughly upon the apparent quantity of 
organic matter in the soil. From five to ten grams of 
pulverized potassium bichromate are then added and 
the whole mixed thoroughly by shaking, care being 
taken to prevent any of the mixture adhering to the 
sides of the flask above the level of the mixture. The 
flask is closed securely by the stopper, and a gentle 
stream of air drawn through the whole apparatus by 
means of the aspirator. When this stream of air has 
been passing for about ten minutes, concentrated sul- 
phuric acid (sp. gr. about 1.83) is slowly and cau- 
tiously run in by means of the dropping funnel until 
the tip of the glass tube for the introduction of air is 
covered. When this point has been reached, and if no 
very vigorous action is taking place, the combustion 
flask is slowly heated until the sulphuric acid com- 
mences to give off fumes. It is held at this temper- 
ature for from five to ten minutes, and then allowed 
to cool slowly, unless there is reason to believe com- 
bustion has not been complete, in w^hich case the tem- 
perature is again raised. Care must be exercised to see 
that a steady current of air be kept passing through 
the apparatus, and that the mixture in the flask be not 
forced back toward the wash bottles. If necessary, 
quite a rapid stream can be drawn through the absorp- 
tion bulbs without much risk of losing the determina- 
tion. It is advisable to have the bulb of the dropping 



58 Soil Physics Laboratory Guide 

funnel empty before commencing the heating, so that 
the tube can be quickly opened. In over 400 exper- 
iments with this method, the flask broke but once, and 
then the dropping funnel could not be opened because 
it contained a quantity of sulphuric acid. A sudden 
large increase of pressure was generated in the flask, 
owing to faulty manipulation. The dangerous char- 
acter of such an accident is sufficiently obvious, but 
with ordinary care, liability of its occurrence is 
extremely small." 

MODIFICATIONS FOR SOILS CONTAINING CHLORIDES AND 

CARBONATES 

In many soils from arid, semi-arid or marshy 
areas there is a considera1)le content of chlorides. By 
following the procedure just described with these soils, 
chlorine gas may be generated, which would be collected 
in the potash bulbs, forming a mixture of the chloride 
and hypochlorite in proportions difficult to estimate 
accurately, and vitiating any attempt to determine the 
amounts of carbon dioxide absorbed. We have made 
a number of attempts to get around this difficulty and 
have found that it can be met quite simply. If the 
bichromate of potash be not mixed with the sample 
before running in the concentrated sulphuric acid, but 
be dissolved in the acid itself and th'e solution be 
slowly and cautiously run in upon the soil, with no 
attempt to heat the mixture until the reaction in the 
flask has proceeded for some time, no hydrochloric 
acid, chlorine nor cliromyl chloride gas is generated, 
or in but very small amounts. The procedure thus 
modified has been used a large number of times with 
artificial mixtures and natural soils, and has proven 
satisfactory, although no expLanation is obvious why 



Soil Physics Laboratory Guide 59 

hydrochloric acid should not be formed and oxidized 
under these conditions. We can only say that, although 
we discovered the fact empirically, we have thoroughly 
tested it with the most gratifying results for the 
method. 

When the amount of chlorides is relatively large, 
it has sometimes been found desirable to treat the 
sample with a small volume of dilute sulphuric aqid, 
adding more acid in small quantities from time to 
time, if necessary, to digest on the steam bath until 
the major part of the hydrochloric acid has been 
removed, and to evaporate as much of the water remain- 
ing as can be done without permitting a noticeable 
action of the solution upon the organic matter. The 
combustion is then carried out as above described. 

With soils which contain carbonates of the alkalies 
or alkaline earths, it would probably be found satis- 
factory first to treat with sulphurous acid to decompose 
the carbonates and drive out the carbon dioxide with- 
out oxidizing the organic matter, and then try to get 
rid of the water and sulphurous acid by evaporating 
to dryness before proceeding with combustion. 

This method presents, however, a number of dif- 
ficult manipulations and requires a great deal of time. 
It has been found, in the experience of this laboratory, 
much more convenient to make a separate determina- 
tion of the carbon dioxide liberated from the carbon- 
ates, by treating a separate sample of the soil with 
dilute sulphuric acid (1:6 by volume), and subtracting 
the amount thus found from the total obtained in the 
combustion. While this method is not entirely free 
from objections for very accurate work, it does unques- 
tionably lead to values with all the accuracy necessary 
for most purposes to which the determination of the 
organic matter in a soil is applicable. 



60 Soil Physics Laboratbry Guide 

In determining the percentage of organic matter 
in the soil from the percentage of carbon dioxide found, 
it is of course necessary to use a conversion factor 
which, multiplied by the weight of CO^, gives the 
weight of organic matter. The factor generally used 
for this purpose is 0.471, based upon Wollny's investi- 
gation of the percentage of carbon in the humus of 
the soil. 

Note — Another method for the determination of 
organic carbon in soils is now used by the Illinois 
Experiment Station. This method, which has been 
found to be quite satisfactory, is described in detail in 
the Journal of the American Chemical Society, Vol. 
26, page 294, and Vol. 26, page 1640. 



EXERCISE 38 

Standardization^ of the Eye-Piece Micrometer* 

Object: To determine the number of spaces on 
an eye-piece micrometer which the soil particles must 
cover to belong to a given grade. 

Directions: In order to separate the particles of 
a given sample of soil into different grades according 
to size, it becomes necessary to measure them with 
sufficient accuracy to determine the grade within which 
limits they fall. As the greater mass of the soil par- 
ticles are microscopic objects or bodies of such small 
dimensions that we cannot measure them accurately 
without first enlarging them sufficiently to permit of 
exact measurements, the compound microscope is used 
for this purpose. 

♦From laboratory notes used at the Illinois College of Agriculture. 



Soil Physics Laboratory Guide 61 

To be able to measure accurately bodies of such 
small proportions, it is essential that we possess a 
stand-ard or measure whose value is known with each 
different degree of magnification resulting from differ- 
ent optical combinations. The stage micrometer is 
well adapted to this purpose and affords a fixed standard 
of comparison where it can be used. There are certain 
conditions, however, which make its use unadvisable 
for general miscroscopic work. One of these is its cost 
and its liability to be broken when it is used for the 
purpose of direct comparison with the object to be 
measured. Another is the mechanical difficulty con- 
nected with the ruling of a stage micrometer which 
shall be accurate and sufficiently close to permit satis- 
factory measurements when used under a high power. 
To avoid these objections as well as to facilitate rapid 
measurements with the microscope and to obviate the 
annoyance of using a stage micrometer in connection 
with the object to be measured, we employ for our 
purpose the eye-piece micrometer, which possesses the 
advantage of being more accurately ruled where high 
powers are desired. 

When using the e3^e-piece micrometer it is placed 
within the ocular of the microscope and above the 
lenses so that it is not enlarged as is the object to 
which it is to be compared. The value of the rulings 
upon the eye-piece micrometer is .1 mm., but as the 
value of the object changes with each combination of 
the microscope, it becomes necessary for us to know 
the magnifying power of each combination of lenses in 
order to determine the size of our object, or to first 
standardize the eye-piece micrometer for each com- 
bination which we are to use by comparing it with a 
standard of known value which is magnified to the 
desired degree. This is done by comparing the eye-piece 



62 Soil Physics Laboratory Guide 

with the stage micrometer and computing the value of 
one space of the eye-piece micrometer for each combi- 
nation of the microscope. When this is known the num- 
ber of the spaces which the soil particles must cover to 
belong to a given grade is determined by dividing the 
value of one space into the size of the particle.- This 
operation is performed for each of the grades and the 
results are arranged in a tabular form together with 
the actual size of the particles and the combinations 
of the microscope used in measuring them for conven- 
ience in saving computation during analysis. 

Each student will make the standardizations and 
compute the value of the eye-piece micrometer with the 
different combinations of the microscope needed to 
measure the particles and tabulate the results as follows : 



Div. 


Name 


Size of Particles 


Spaces of 
Micrometer 


Objective and 
Ocular 


1 

2 
3 
4 
5 
6 
7 


Tine gravel 
Coarse sand 
Medium sand 
Fine sand 
Very fine sand 
Silt 
Clay 


2 to 1 mm. 
1 to .5 mm. 
.5 to .25 mm. 
.25 to .1 mm. 
.1 to .05 mm. 
.05 to .005 mm. 
.005 to .0001 mm. 







EXERCISE 39 

Mechanical Analysis of Soils 

Object: To determine the percentage of gravel, 
fine gravel, coarse, medium, fine and very fine sand, 
silt and clay in a sample of "fine earth." 

Directions : 

1 — Thoroughly mix, upon a heavy paper or oil- 
cloth, the sample of air-dried soil to be analyzed ; take 
from the well-mixed mass about 100 grams of soil and 



Soil Physics Laboratory Guide 63 

weigh accurately ; roll the sample with a wooden rolling 
pin and sift it with a 2 mm. sieve. Weigh all small 
stones- and pebbles which do not pass the sieve and 
determine the percentage of this material. 

2 — Place about ten grams of the sifted soil which 
is designated as "fine earth" in a crucible and dry to a 
constant weight in an oven maintained at 110 degrees C. 

3 — Place five grams of the water-free soil in a 
shaker bottle and add about 75 c. c. of distilled water 
and ten drops of .ammonia. Exercise care in weighing 
the sample of soil and in transferring it to the bottle. 

4 — Place the bottle in the shaking apparatus and 
agitate it until a microscopic examination of the 
contents shows that the soil particles are completely 
separated and no compound particles exist. "When 
this condition is reached the individual particles will 
appear clear and semi-transparent in the field of the 
misroscope, while any remaining compound particles 
will be darker and variously colored from reflected 
light. This may require from twelve to twenty-four 
hours, or even longer, depending very much upon the 
nature of the soil. As the determination is quantita- 
tive but a small amount of the liquid is taken from the 
bottle with a capillary pipette, and mounted on a slide 
for examination. When the examination is complete, 
the slide and cover glass are carefully rinsed with dis- 
tilled water back into the shaker bottle to recover the 
small portion of soil taken. Great care is necessary 
throughout the analysis to prevent the loss of any part 
of the sample and for the purpose of comparison and 
greater accuracy in results, duplicate samples are used 
of each soil analyzed." 

5 — When no compound particles are found in the 
samples, transfer the contents of the shaker bottles into 
centrifuge tubes. 



64 Soil Physics Laboratory Guide 

6 — Place the tubes in the centrifuge, care being 
taken to have the weight evenly distributed so that the 
apparatus will run steadily. Rotate the tubes in the 
centrifuge for two or three minutes at a speed 
sufficiently high to throw down all particles except those 
which belong to the grade listed as clay. To determine 
the speed and time required for this operation, examine 
the suspended material with the microscope, taking 
the sample and mounting it as described above. 

7 — When it is found that no particles larger than 
.005 mm. are left in suspension, carefully decant the 
liquid in each tube into a weighed 400 c. c. beaker, 
which is numbered to correspond with the number of 
the tube. 

8 — Nearly fill the tubes with distilled water which 
is delivered with sufficient pressure to thoroughly stir 
up the contents of the tubes. 

9 — Continue to rotate the centrifuge and decant 
until the contents of each tube are free from particles 
which belong to the grade designated as clay. Care 
must be taken to determine quite accurately just the 
time required for the particles larger than .005 mm. 
to settle, for if the centrifuge is rotated too long, a 
portion of the clay also goes down and the time 
required to complete the separation is thus greatly 
lengthened. 

10 — Evaporate the contents of the beakers to dry- 
ness on the water bath ; then dry the residual matter 
in the beakers to a constant weight in the oven at 110 
degrees C. and determine the percent of clay in the 
sample of soil. 

11 — After the clay particles have been separated 
as described above, place the tubes in a rack and thor- 
oughly stir the contents by filling the tubes with dis- 
tilled water which is delivered under pressure. 



Soil Physics Laboratory Guide 65 

12 — Examine the suspended material with the 
microscope and in this way determine the length of 
time required for all the particles to settle which are 
larger than .05 mm. Decant into large beakers which 
are numbered to correspond to the number of the tubes. 
Eepeat the operation of stirring the contents of the 
tubes and decanting until all of the silt particles are 
removed. 

13 — Set aside the beakers containing the silt for 
twelve hours or more, or until all of the silt has settled. 
Then decant nearly all of the water from each beaker; 
carefully transfer the silt to a weighed and numbered 
porcelain or nickel dish and evaporate to dryness on 
the water bath. Dry the silt in the oven at 110 degrees 
C. to a constant weight and determine the percent of 
silt in the sample of soil. 

14 — Wash the sand which is left in the tubes after 
the clay and silt are removed, into weighed and num- 
bered crucibles; evaporate to dryness on the water bath 
and dry to a constant weight in the oven at 110 degrees 
C. Weigh and record as total sand. 

15 — Separate the sand into the various grades by 
the use of a series of sieves fitted with bolting cloth 
and determine the percent of each grade in the sample 
of soil. 



66 Soil Physics Laboratory Guide 

16 — Make a mechanical analysis of the soils 
furnished by the instructor and tabulate tne data 
as follows: 



MECHANICAL ANALYSIS 
Sample No. Date_ 



Gravel > 2 mm. 



Percent 



Analysis of 5 grams of soil < 2 mm. 



No. Dish Sands l-5_ 

Wt. Dish & Soil 

Weight of Dish 

Weight of Soil 



No. Dish Silt 6_ 



No. Dish Clay 7_. 





Diameter 
mm. 


Weight 
grams 


Percent 


1 

2 
3 

4 
5 
6 

7 


2 -1 
1 - .5 
.5 - .25 
.25 - .1 
.1 - .05 
.05 - .005 
< .005 






Total 









Soil Physics Laboratory Guide 67 




Plate 12 

MECHANICAL SHAKER USED IN PREPARING SOILS FOR 
MECHANICAL ANALYSIS 



The shaker consists of a platform which carries the 
trays resting upon four three-quarter-inch iron supports 
which are thirty inches high. 

The trays are divided into individual compartments, 
each tray holding eight bottles which correspond to the 
number of samples usually analyzed at a time. The 
trays are made of half-inch material. They are sixteen 



68 Soil Physics Laboratory Guide 

inches long, nine and one-quarter inches wide and three 
inches deep outside measurement. 

Each tray has a pin placed at either end, whieh fits 
into holes in the tray above it, so that four or more trays 
may be placed upon the shaker at one time. 

The shaker is driven by a 110-volt, oncrsixteenth- 
horse power motor which is belted to a fiber worm reduc- 
ing gear provided with a crank to which the shaker is 
connected as shown in the illustration. The motor is 
provided with a regulating rheostat to adjust the speed 
when the shaker is not fully loaded. 

The 110-volt motor with shaker attachment costs 
about twenty-five dollars. 

The bottles for use in the shaker may be purchased 
from Whitall Tatum Company, Philadelphia. They are 
known as eight-ounce sterilizing bottles, flint glass, 
graduated. They require E & A rubber stoppers No. 1. 
They cost about four dollars per gross. 



Soil Physics Laboratory Guide 69 




Plate 13 

CENTRIFUGAL MACHINE USED IN MECHANICAL ANALYSIS OF 

SOILS AND TANK FOR THE SUPPLY OF DISTILLED 

WATER UNDER PRESSURE 



The following description of the centrifugal appa- 
ratus which is shown in the illustration is taken from 
Bulletin No. 24, Bureau of Soils : 

"The centrifugal apparatus consists of a 110-volt, 
sixteen-inch fan motor mounted with its shaft in a ver- 
tical position, to which is attached a spider carrying eight 
trunnioned frames. The distance from the center of the 
motor shaft to the center of the trunnion screws is 
10 cm., and the depth of the trunnioned racks is 
15 cm. The centrifugal tubes consist of large, heavy 
glass test tubes, 18x3 cm., which are supported in the 
trunnioned racks. The aperture in the upper ring of 
the support Is made large enough to admit the test 
tube readily, while the opening in the lower ring is 
smaller than the tube and is faced with a felt cushion 
on which the tube rests. It is important that the tubes 
should be thoroughly annealed; otherwise breakage is 
apt to occur under the strain to which they are subjected 



70 Soil Physics Laboratory Guide 

during rotation. To protect the operator from such 
accidents a guard surrounds the movable portion of the 
machine. 

"Th€ motor is provided with a rheostat in its base, 
giving four different speeds, which enables one to start 
the motor slowly and bring it gradually up to full speed. 
The machine, when loaded and running at full speed, 
requires about one minute to stop after the circuit is 
opened. To avoid this delay, the motor is provided with 
a reversing switch, by means of which the direction of 
the current through the armature may be reversed and 
the motor brought quickly to rest. Before stopping the 
machine in this way, the rheostat should be set at the 
first speed, then slowly moved to the second or third in 
order that the motor may not be subjected to too great 
mechanical and electrical strain in the reversing process." 

A jet of distilled water under considerable pressure 
is needed to wash the samples from the shaker bottles 
and in bringing the soil into suspension after it has been 
packed into the bottom of the tubes by centrifugal action. 
For this purpose, a thirty-gallon tank is located near the 
centrifugal machine. The tank is filled about half full 
of distilled water and air is admitted from the pressure 
cock. The water is drawn from the tank through a pipe 
and rubber tubing as shown. If the laboratory is not 
provided with compressed air a large bicycle pump may 
be used. The tank and fixtures are not expensive and 
have been found very satisfactory. 



Soil Physics Laboratory Guide 



71 




Plate 14 



NEST OF SIEVES USED TO SEPARATE SAND INTO THE 
VARIOUS GRADES 



The large brass sieve shown in the illustration is 
six inches in diameter with 2 mm. meshes. 

The nest of sieves is made of brass and is four 
inches in diameter. The two upper sieves have circular 
perforations 1 mm. and .5 mm. respectively. The two 
lower sieves are made of silk bolting cloth stretched over 
brass frames and held in position by slip rings. 

The sieves shown in the illustration are fitted with 
silk bolting cloth. 

The bolting cloth may be purchased from B. F. Starr 
& Co., Baltimore, Md. 



72 Soil Physics Laboratory Guide 

EXERCISE 40 

Mechanical Analysis of Soils by the Beaker 

Method 

Directions : 

1— Thoroughly mix upon a heavy paper or oil- 
cloth, the sample of air-dried soil to ])e analyzed; take 
from the well-mixed mass about 100 grams of soil and 
weigh accurately. 

Eoll the 100-gram sample with a wooden rolling- 
pin and sift it with a 2 mm. sieve. Weigh all small 
stones and pebbles which do not pass through the sieve 
and determine the percentage of this material. 

2 — Place about thirty grams of the sifted soil 
which is designated as "fine earth" in a porcelain dish 
and dry to a constant weight at 110 degrees C. 

3 — Place twenty grams of the water-free soil in a 
shaker bottle and add about 75 c. c. of distilled water 
and fifteen drops of ammonia. Exercise care in 
weighing the sample of soil and in transferring it to 
the bottle. 

4 — Place the bottle in the shaking apparatus and 
agitate it until a microscopic examination of the con- 
tents shows that the soil particles are completely 
separated. (See the preceding exercise for the method 
of making this examination.) 

5 — When no compound particles are found in the 
samples, transfer the contents of the shaker bottle into 
a 400 c. c. beaker ; add about 200 c. c. of distilled water 
and stir thoroughly with a glass rod. 

6 — Allow the contents of the beaker to settle until 
all particles larger than .05 mm. have subsided. This 
is determined by examining a drop of the turbid liquid 



Soil Physics Laboratory Guide 73 

which is drawn from near the bottom of the beaker 
with a capillary pipette, under a- microscope fitted 
with an eye-piece micrometer. 

7 — When all of the particles larger than .05 mm. 
have subsided, decant the turbid liquid containing the 
silt and clay into a larger beaker. Repeat this oper- 
ation until all particles smaller than .05 mm. have 
been removed. 

8 — Transfer the sediment to a weighed evapor- 
ating dish, dry to a constant weight in the oven at 110 
degrees C. and weigh as total sand. 

9 — Further separate the sand into the various 
grades by passing it through a series of brass sieves 
four inches in diameter which fit into each other. The 
first sieve has circular openings 1 mm. in diameter 
and the second .5 mm. The particles passing through 
the lower sieves are sifted through screens of No. 5 and 
No. 13 bolting cloth. 

10 — Allow the turbid liquid in the beaker contain- 
ing the silt and clay to settle until the microscope 
shows that all particles larger than .005 mm. have 
settled. 

11 — Decant the liquid containing the clay into a 
third beaker of about 2000 c. c. capacity. Stir the 
sediment in the bottom of the beaker with more water, 
allow to settle and decant. Repeat this operation until 
all particles smaller than .005 mm. are removed. 

12 — Wash the silt into a small weighed porcelain 
dish. Evaporate to dryness on the water bath. Dry 
to a constant weight in the oven at 110 degrees C. 
and weigh. 

13 — Accurately measure the clay water in the 
third beaker and, after thoroughly stirring, take an 



74 Soil Physics Laboratory Guide 

aliquot portion, evaporate to dryness on the water bath, 
dry to a constant weight in the oven and weigh. 

14 — Make a mechanical analysis of the soils fur- 
nished by the instructor and tabulate the data as in 
the preceding exercise. 




Plate 15 



STUDENTS' LABORATORY DESK 



The illustration shows one end of a desk used in the 
Soil Physics Laboratory at the Iowa State College. The 
desks are thirty-three inches high, sixty inches long from 
the end to the center of the sink, and have a total width 
of fifty-six inches. Students work on both sides of 
these desks. 

The space from the end of the desk to the center of 
the sink is provided with two sets of drawers and lockers. 
This arrangement enables the class to work in two sec- 
tions ; the student in each section has a drawer and locker 
in which to store and lock up his apparatus and has five 
feet of desk room during his laboratory period. 



Soil Physics Laboratory Guide 75 

Tlie desks are supplied with sinks, gas cocks and 
water cocks as shown. All of the plumbing is exposed 
and thus is easily kept in repair. The lower shelf is five 
inches wide and is five inches above the desk. The upper 
shelf is six inches wide and is fifteen and one-half inches 
above the desk. 



APPENDIX 

Laboratory Notes 

Each student should keep a careful record of his 
laboratory work in a well-bound notebook. This book 
should always be at hand during the progress of an 
experiment and all data should be recorded promptly. 
It is never safe to record weights or data of any kind on 
loose sheets of paper. They are too often lost. 

The outlines for the tabulation of data which are 
printed in the guide are for the direction of the student. 
No figures should be entered in the guide but the data 
should be recorded in the notebook as indicated in the 
outlines. 

The student should study each exercise carefully, 
before beginning work^ in order to obtain a clear under- 
standing of the nature of the exercise, the directions 
to be followed and the data to be secured. All of the 
experiments should be done in duplicate. 

The laboratory directions should not be copied into 
the notebook but all of the data should be recorded 
in tabular form and a brief, concise statement should 
be made covering the following points : 

1 — The object of the experiment. 

2 — The materials used. 

3 — The apparatus employed. 

4 — The manner of conducting the experiment. 

5 — The facts noted during the progress of the 

experiment. 
6 — The conclusions which are drawn, and 

finally suggestions regarding any changes 

in the experiment. 



Soil Physics Laboratory Guide 77 

With nearly every experiment, questions are asked ; 
the answers to these questions should be given in full 
in the notebook. The student should refer to author- 
ities on Soil Physics as an aid in answering some of the 
questions and his statements should embody a com- 
plete, comprehensive answer. 

Each experiment should be written up at the time 
it is performed. Confusion and loss of time inevitably 
follow an effort to write up several experiments which 
have been worked out but only the weights or measure- 
ments recorded. 

The notebook should be kept in a neat and orderly 
way and should always be ready for examination by the 
instructor. The student should never fail to correct 
the errors which are marked by the instructor, and it 
is far better to perform a limited number of experi- 
ments correctly than to pass over a large number in a 
slip-shod manner. 



Precautions to Be Used in Weighing 

The following directions for weighing are taken 
from the laboratory notes used in Johns Hopkins 
University : 

1 — Sit directly in front of the center of the 
balance so as to avoid parallax while observing the 
movements of the pointer. 

2 — See that the balance is level. 

3 — Eelease and arrest the beam with a slow and 
steady movement of the hand. Jerky movements are 
sure to injure the knife edges. The beam should be 
arrested only when it is in a horizontal position. 

L OF a 



78 Soil Physics Laboratory Guide 

4 — Avoid giving to the pans any rotary motion 
in a horizontal direction and all other movements 
which would cause a knife edge to scrape on its 
^ bearing. 

5 — Release the pans before releasing the beam. 

6 — Arrest the beam and pans before placing any- 
thing upon or removing anything from the latter. 

7 — Place the object to be weighed and the larger 
weights in the middle of the pans. 

8 — See that the rider is not so near the beam as 
to be hit by it while swinging. 

9 — All weighings should be made with the balance 
case closed. 

10 — If the beam does not begin to swing as soon 
as it is released, set it in . motion by wafting the air 
over one of the pans with the hand or by raising and 
releasing it again. 

11 — Hot objects cannot be correctly weighed, 
owing to the upward draughts which they create about 
the pans on which they rest. They may also, through 
their heating effects upon the beam, produce a change 
in the relative lengths of the arms. 

12 — Hygroscopic and volatile substances, also those 
which absorb carbon dioxide from the air, must be 
weighed in closed vessels. If the vessels have been 
tightly closed while hot, there may be diminished 
pressure within, in which case they must be opened 
for a moment before weighing. 

13 — All substances which are exposed to the air 
condense moisture on their surface to an extent which 
sensibly affects their weight. The amount of moisture 
thus condensed varies with the humidity of the atmos- 
phere; hence a substance which is transferred from a 



Soil Physics Laboratory Guide 79 

desiccator to the balance pan will gain weight for a 
time, while one which is brought from a clamper 
atmosphere than that within the balance case will 
lose weight. By keeping drying reagents in the case, 
it is endeavored to maintain a fairly uniform condition 
of humidity, and thus to reduce the errors from this 
source to a minimum. Powdered substances which 
have been dried in a hot bath, or in a desiccator, should 
be weighed in closed vessels; since, owing to the great 
surface which they present to the air, they condense 
large amounts of moisture. In all cases, it is neces- 
sary to be sure that the object which is being weighed 
has ceased to gain or lose weight before taking the 
final reading. 

14 — An object which, like glass, is likely to become 
electrified by friction, should not be wiped or brushed 
immediately before weighing. Glass and quartz weights 
often become strongly electrified when lifted out of 
their places in the box in which they are kept. 

15 — Long tubes and other objects not easily 
centered on the pans should be suspended from the 
hooks above the pans. 

Weights and Measures, with Equivalents 

METRIC 

Meter (Unit of Length) Millimeter (mm.) = 0.001 meter 

Centimeter (cm.) = 0.01 meter 

Kilometer = 1000 meters 

Micron = 0.001 millimeter 

Gram (Unit of "Weight) Milligram (mg.) = 0.001 gram 

Kilogram (kilo) = 1000 grams 

Liter (Unit of Capacity) Cubic Centimeter = 0.001 liter 

1 millimeter - 1 0.03937 (or 1-25 approx.) inch 
1 millimeter - | ^^^ microns 

1 oentimeter - I ^•^^^' i^^' ^'^ approx.) inch 
1 centimeter — | o.0328 foot 

1 metPr - \ ^^'^^ ^"<^^®^ 

1 meter - 1 3 93 feet 

t -r, r.^ i 1-25000 inch 

1 micron = | ^ qq^ millimeter 



80 Soil Physics Laboratory Guide 

'e-- = {SS7o"und} Avoir. 

1 kilogram = {S'J„rc,r!*™-. 

( 1.056 (or 1 approx.) quart 
1 liter = I 61.02 cu. inches 

( 1000 cu. centimeters 

1 sq. millimeter = 0.00155 ) 

1 sq. centimeter = 0.1550 [ sq. inches 

1 sq. meter = 1550 ) 

1 sq. meter = 10.76 sq. ft. 

1 cu. millimeter = 0.00006 )„ ■ , 
1 cu. centimeter = 0.0610 | ^"* ^'^^^ 
1 cu. centimeter = 0.001 liter 

1 cu. meter = I S ^''- ^^-^ ^... 

\ 61025.4 cu. inches 

1 inch = 25.399 millimeters 

1 sq. inch = 6.451 sq. centimeters 

1 cu. inch = 16.387 cu. centimeters 

1 foot = 30.48 centimeters 

1 sq. foot = 0.093 sq. metej 

1 cu. foot = 0.028 cu. meter 

AVOIRDUPOIS WEIGHT 
1 pound = 16 ounces 
1 ounce = 28.35 (or approx. 30) ) „-.„.„„ 
1 pound = 453.59 (approx. 500) | S'^ams 

FORMULAE, ETC. 
A cubic foot of water weighs 62.42 pounds 

Temperature: Centigrade degree= 0.555 (Fahr.-32°); 
95° F. = 0.555 (95°-32) = 34-97° C. 
Fahrenheit degree = 1.8 x Cent, -f 32* 
80° C. = 1.8 X 80 + 32 = 176° F. 

Area of circle = 7rr*, where r = radius, tt = 3.1416 

Circumference of circle = 27rr 

Circumference 
Radius=- 



27r 

Area of cylinder = 27rr h ; where r — radius of cross 
section, and h= hight or length 
Volume of cylinder = irr^h 



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